30分析此句：As is mentioned above,the number of the students in s

the number of the students in senior high school is increasing是主句.
As is mentioned above是个定语从句,
as是关系代词,在从句中作主语,代替整个主句the number of the students in senior high school is increasing.
全句意思是：
正如上面所提到的一样,高中生的数量在增加.